Experimental Measurement of Single-Wall Carbon Nanotube Torsional Properties

We report on the characterization of nanometer-scale torsional devices based on individual single-walled carbon nanotubes as the spring elements. The axial shear moduli of the nanotubes are obtained through modeling of device reaction to various amounts of applied electrostatic force and are compared to theoretical values

Resonant Oscillators with Carbon-Nanotube Torsion Springs

We report on the characterization of nanometer-scale resonators. Each device incorporates one multiwalled carbon nanotube (MWNT) as a torsional spring. The devices are actuated electrostatically, and their deflections, both low frequency and on resonance, are detected optically. These are some of the smallest electromechanical devices ever created and are a demonstration of practical integrated MWNT-based oscillators. The results also show surprising intershell mechanical coupling behavior in the MWNTs

Epicyclic orbits in a viscous fluid about a precessing rod: Theory and experiments at the micro- and macro-scales

We present experimental observations and quantified theoretical predictions of the nanoscale hydrodynamics induced by nanorod precession emulating primary cilia motion in developing embryos. We observe phenomena including micron size particles which exhibit epicyclic orbits with coherent fluctuations distinguishable from comparable amplitude thermal noise. Quantifying the mixing and transport physics of such motions on small scales is critical to understanding fundamental biological processes such as extracellular redistribution of nutrients. We present experiments designed to quantify the trajectories of these particles, which are seen to consist of slow orbits about the rod, with secondary epicycles quasicommensurate with the precession rate. A first-principles theory is developed to predict trajectories in such time-varying flows. The theory is further tested using a dynamically similar macroscale experiment to remove thermal noise effects. The excellent agreement between our theory and experiments confirms that the continuum hypothesis applies all the way to the scales of such submicron biological motions

Thin-foil magnetic force system for high-numerical-aperture microscopy

Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 μm paramagnetic particle and 13 nN on a 4.5 μm paramagnetic particle, forces over the full 4π sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 μm xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function

Three-dimensional force microscope: A nanometric optical tracking and magnetic manipulation system for the biomedical sciences

We report here the development of a three-dimensional (3D) magnetic force microscope for applying forces to and measuring responses of biological systems and materials. This instrument combines a conventional optical microscope with a free-floating or specifically bound magnetic bead used as a mechanical probe. Forces can be applied by the bead to microscopic structures of interest (specimens), while the reaction displacement of the bead is measured. This enables 3D mechanical manipulations and measurements to be performed on specimens in fluids. Force is generated by the magnetically permeable bead in reaction to fields produced by external electromagnets. The displacement is measured by interferometry using forward light scattered by the bead from a focused laser beam. The far-field interference pattern is imaged on a quadrant photodetector from which the 3D displacement can be computed over a limited range about the focal point. The bead and specimen are mounted on a 3D translation stage and feedback techniques are used to keep the bead within this limited range. We demonstrate the system with application to beads attached to cilia in human lung cell cultures